1. Field of the Invention
The present invention relates to a secondary battery state detecting apparatus and a secondary battery state detecting method.
2. Background of the Invention
In recent years, automobiles or the like tends to have an increased number of electric devices operated with an electric power accumulated in a secondary battery, and devices associated with the safety in running, such as an electric steering and an electric brake, also tend to be driven by the secondary battery. Accordingly, there is an increasing need in accurately knowing a state of charge (e.g., SOC: State of Charge) of the secondary battery.
In general, when the secondary battery is stable, there is a proportional relationship between its open circuit voltage (OCV) and the state of charge. Accordingly, the state of charge can be estimated by detecting the open circuit voltage. However, in a case of a vehicle such as an automobile, at the time of start-up of an engine, since there is an electric power supply from the secondary battery to each load and also an electric power supply from the alternator to the secondary battery, charging and discharging occur repeatedly. In a rechargeable battery after charging and discharging, the proportional relationship between the open circuit voltage and the state of charge does not hold, since the rechargeable battery is affected by generating and disappearing reactions of ions at a surface of a battery plate by an electrochemical reaction and movement of ions by diffusion or convection of an electrolyte.
Japanese Laid-Open Patent Application Nos. 2009-2691 and 2009-300209 disclose techniques in which an open circuit voltage and a state of charge are accurately estimated even after charging and discharging.
As for an automobile or the like, when the starting up of an engine has become difficult due to an insufficient capacity of the secondary battery, a so-called “jump start” may be carried out as an emergency measures by directly connecting terminals of a secondary battery of a disabled vehicle to terminals of a second battery of a rescue vehicle with a cable, and starting up the engine with a power supplied by the rescue vehicle.
When such a jump start is carried out, since the terminals are connected to each other and an electric current bypasses a current sensor, for example, with the techniques disclosed in Japanese Laid-Open Patent Application Nos. 2009-2691 and 2009-300209, influences by polarization and/or stratification cannot be estimated accurately. Therefore, there is a problem that an estimated open circuit voltage and state of charge include errors. Also, other than the jump start, there may be a case where, for example, a secondary battery is charged by directly connecting a charger to the secondary battery, and in such a case, there is also a problem that the estimated open circuit voltage and/or the state of charge include errors.
On a disabled vehicle side, “blind charging” occurs in which the secondary battery is charged without passing through a current sensor, and on a rescue vehicle side, “blind discharging” occurs in which the secondary battery is discharged without passing through a current sensor. When such blind charging or blind discharging has occurred, an influence by polarization and/or stratification cannot be estimated accurately with the techniques disclosed in Japanese Laid-Open Patent Application Nos. 2009-2691 and 2009-300209. Therefore, the estimated open circuit voltage and state of charge include errors. Therefore, it is necessary to detect occurrences of blind charging and blind discharging and to perform correction for each of them. However, a technique for detecting blind charging and blind discharging did not exist in the related art.
Therefore, an object of the present invention is to provide a secondary battery state detecting apparatus and a secondary battery state detecting method that can accurately detect the state of the secondary battery and also detect an occurrence of blind charging and blind discharging, even if an irregular charging-discharging that bypasses a current sensor has been carried out.